Retainers usually cap your margins at 30% because they're tied to headcount....

https://dibz.me/blog/why-a-handful-of-european-seo-agencies-stopped-being-agencies-and-1138

Retainers usually cap your margins at 30% because they're tied to headcount. Start treating your agency like a lab to build tools that solve your own manual work. This lets you trade services for software and push those margins past 70%.